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<h1>SQL MID() 函数</h1>
<h2>MID() 函数</h2> <p>MID() 函数用于从文本字段中提取字符。</p> <h3>SQL MID() 语法</h3> <div class="code notranslate"><pre><code class="language-sql"><div> SELECT MID(column_name,start[,length]) FROM table_name;</div></code></pre></div> <br/><table class="reference notranslate">
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<th align="left" valign="top" width="20%">参数</th> <th align="left" valign="top" width="80%">描述</th> </tr>
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<td valign="top">column_name</td> <td valign="top">必需。要提取字符的字段。</td> </tr>
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<td valign="top">start</td> <td valign="top">必需。规定开始位置（起始值是 1）。</td> </tr>
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<td valign="top">length</td> <td valign="top">可选。要返回的字符数。如果省略，则 MID() 函数返回剩余文本。</td> </tr>
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<h2>演示数据库</h2> <p>在本教程中，我们将使用众所周知的 Northwind 样本数据库。</p> <p>下面是选自 "Customers" 表的数据：</p> <table class="reference notranslate">
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<th>CustomerID</th> <th>CustomerName</th> <th>ContactName</th> <th>Address</th> <th>City</th> <th>PostalCode</th> <th>Country</th> </tr>
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<td>1<br/><br/>
</td> <td>Alfreds Futterkiste</td> <td>Maria Anders</td> <td>Obere Str. 57</td> <td>Berlin</td> <td>12209</td> <td>Germany</td> </tr>
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<td>2</td> <td>Ana Trujillo Emparedados y helados</td> <td>Ana Trujillo</td> <td>Avda. de la Constitución 2222</td> <td>México D.F.</td> <td>05021</td> <td>Mexico</td> </tr>
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<td>3</td> <td>Antonio Moreno Taquería</td> <td>Antonio Moreno</td> <td>Mataderos 2312</td> <td>México D.F.</td> <td>05023</td> <td>Mexico</td> </tr>
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<td>4<br/><br/>
</td> <td>Around the Horn</td> <td>Thomas Hardy</td> <td>120 Hanover Sq.</td> <td>London</td> <td>WA1 1DP</td> <td>UK</td> </tr>
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<td>5</td> <td>Berglunds snabbköp</td> <td>Christina Berglund</td> <td>Berguvsvägen 8</td> <td>Luleå</td> <td>S-958 22</td> <td>Sweden</td> </tr>
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<h2>SQL MID() 实例</h2> <p>下面的 SQL 语句从 "Customers" 表的 "City" 列中提取前 4 个字符：</p> <div class="example margin-b-10"> <h2 class="example">实例</h2> <pre><code class="language-sql"><div class="example_code notranslate"> SELECT MID(City,1,4) AS ShortCity<br/>FROM Customers; </div></code></pre> </div> <div class="text-center padding-10 margin-t-5">
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